I was given a very simple schematic of a starting spud gun, with a 4" by 36" chamber and a 2" by 36" barrel, with a lantern striker for ignition, a 4" to 2" reducer between the chamber and barrel, and Aqua Net Hairspray propellant.
I perused the wiki for information, and learned about CB ratios; according to the wiki, the optimal ratio is between .6 and .8, and, using some math, I figured out the optimal chamber length for me is 5.4". Is this correct?
Second off, what are some methods for mounting a fan onto the chamber? would it go in the end and be exposed? Pictures provided would be fantastic.

Finally, as the hair spray method doesn't provide accurate results per launch, how would a fuel injector work, and with what kind of fuel?
Sorry if there are too many questions, and thank you for your time! =)